Constant temperature apparatus



Nov. 3, 1942- c. F. BALDWIN CONSTANT TEMPERATURE APPARATUS Fiied June V22, 1940 F? Besuch/vimlv za z Fgl.

Patented Nov. 3,-'.1942

2,301,007 CONSTANT TEMPERATURE APPARATUS ohm F. Baldwin, Schenectady, N. Y., minor to General Electric Company, a corporation o! New York Application June 22, 1940, Serial No. 341,976

(crm-327) Claims.

This invention relates to heating means and more particularly to apparatus for maintaining a device at a constant temperature.

Certain devices, whose operating characteristics change upon change in temperature, are desirably maintained at a constant temperature for better operation. It -is an object of my invention to provide means to maintain the temperature of `a. device within -very narrow limits even when ambient temperatures change over wide limits.

It is a more particular object of my invention to provide apparatus to maintain the temperature of a device within one unit of temperature change when the ambient temperature varies as much as 90 or even 100, or more, units of temperature. My present invention is especially suited to maintain electric circuit elements,'such as piezo electric vibrators, at highly constant temperatures under adverse conditions and over long periods of time. The features of my invention ,which I believe to be novel are set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation, 'together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a view, partlyl in section, of apparatus embodying my invention; Fig. 2 is.,a detailed sectional view of a portion of Fig. 1;- Fig. 3 is a detailed sectional view ol' a modified form of a portion of Fig. 1; Fig. 4v is a sectional view of a device especially adapted for use in my invention; Fig. 5 is a modication of the device illustrated in Fig. 4; Fig. 6 is a modified form of the apparatus of Fig. 1; and Fig. 7 illustrates an additional modification oi apparatus embodying my invention.

Referring to Fig. 1 of the drawing, I have shown therein a hermetically sealed'vessel I0, having electric terminals II, I2, I3 and I4 extending through one wall Il thereof, housing a unit I6 comprising a piezo electric vibrator anda pair of electrodes, to be described later. The unit I6 is attached in good thermal contact to a supporting member or post I l, which is formed of copper and is supported from the end wall' I6 of the vessel I0 by a pair oi' electric'insulators I6 and I3, mounted on the end wail I6.

Electric circuit connections to the piezo electric unit Il are made through contact prong II, a conductor 2l, the unit I6, a conductor 2i, and contact prong I4. The conductors 2li and 2i are connected respectively to opposite electrodes of 22 and the unit I6.

the unit I6. These vconductors should be arranged to allow little heat to flow to and from the unit I6 therethrough. In certain situations,

.for example, it may be found desirable to make them of a size and of material having high resistance to heat iiow. Nickel wires whose diameter is. ve thousandths of an inch have been used.

Heating means comprising a resistance heater unit 22 is formed around the supporting member Il in the path of heat iiow therethrough between thel unit I6 and the wall I5 of the vessel I0. A thermostat 23, having a movable bi-metallic strip 24 `and anadjustable stationary contact 25, is attached to the supporting member I1 at a point between the heater 22 and the unit I6. A source of voltage, not shown, is connected between the terminals I2 and I3 to form a circuit through that source, terminal I2, a conductor 26, the heater 22, the copper supporting member I1,-the movable bimetallic strip 24, the adjustable contact 25, a conductor 2l, and the terminal I3. This circuit may of course be arranged so as not to include post Il whereby the heater circuit and circuit for unit I6 may be isolated.

In the structure so far described, heat flows from heater 22 to unit I6 primarily through the copper supporting post I1, and heat flows from the unit I6 to surrounding regions of lower tem-, perature primarily by convection and radiation.

The thermostat 23 is responsive to some ther.- mal condition, such as the temperature, of the supporting member or post Il between the heater When the temperature of the post at that pointis below a predetermined value, the circuit through the heater 22 is completed and heat is applied thereby to the member I1. Due to the fact that heat flows to the unit I6 principally through the supporting member. I'I,

the described arrangement Vof the unit I6, the

thermostat 23, and the heating means 22 with lthrough the supporting member Il to the unit I6.

There remains then only one path .through which heat can leave the unit I6, that is, by radiation or convection, by which the amount of heat leaving unit I6 is minimized. There is thus a minimum din'erence in temperature between unit I6 and thermostat 24. Since thermostat 24 is char- Conversely,

acteristically at a constant temperature and unit I5 differs therefrom in minimum amount, the temperature of unit I6 is substantially constant.

A further advantageous eilect arises from the arrangement of parts describedr in that the change in average temperature of the unit I5 is very small upon large changes in ambient temperature. The ratio of change of ambient temperature to change in average temperature of the unit |5 is sometimes designated Icontrol ratio. It has been found that with apparatus constructed as described, control ratios have been obtained as large as 75 or 100 or even higher. It is thought that the reason for this effect is that the principal path of heat flow to the unit is from the source of heat past the thermostat which maintains the unit I5 at constant temperature.

In Fig. 2, which illustrates the structure of the thermostat 23, one end of the bimetallic element 24 is attachedv by means of a bolt 28 to the supporting post I1. An insulating block 29 is fastened to the post I1 and the adjustable contact 25, which is screw-threaded therein, is fastened in place by ,a lock nut 35. The contact 25 extends through a hole 3| in the post I1, so that it is insulated therefrom. Contacts 32 are provided at the places on the bimetallic element 24 and the contact 25 through which a conductive connection is made.

It has been found that air is a very satisfactory filler for the vessel l5 as it neither causes excessive heat loss from the unit I5 by convection, nor causes destructive arcing at the contacts 32, which are preferably made of a platinum-iridium alloy. It is, however, entirely within the scope of the invention to fill the .vessel I5 with gases other than air. or to evacuate it.

The above described thermostat 23 is quite satisfactory in locations where the apparatus ernbodying my invention is not subject to sudden shocks. However, in certain locations, such as in airplanes and the like, it is desirable to assure more stable operation of the thermostat by providing snap action therefor. Also in case the heater is energized with continuous current, snap action may be desirable. Fig. 3 illustrates a thermostat designed to this end. The bimetallic element 24 is made longer and is bent around to the opposite face of the post |1, where it is fastened by the bolt 25. This extra length of the member 24 gives it greater ilexibility. On the end of the adjustable contact 25 there is fixed a permanent magnet 33. If the bimetallic member 24 is not made of ferro-magnetic material, an amature may be provided thereon. For example, a contact tip 34 on the bimetallic member 24 may cover a ferro-magnetic armature to be attracted by the permanent magnet 33. The magnet 33 is likewise covered by a contact tip 35, which cooperates with the contact tip 34. 'I'he magnet 33 and its armature cooperate in a well known way, so that. as the member 24 approaches the magnet 33. they suddenly snap together. as the bimetallic member 24 is stressed more and more highly to move away from the magnet 33, a point is reached at which the bimetallic member 24 suddenly snaps away from the permanent magnet 33.

Fig. 4 illustrates a cross sectional view o1' the unit I5. A supporting electrode 45, which is attached in good heat transfer relation vto the supporting member I1. cooperates with a body 4| of ceramic material to support a quartz crystal pieno electric vibrator 42 closely adjacent to the electrode u. The e1eetrode an a preferably 75 formed of stainless steel, which is carefully ground fiat so as to lie in good thermal conducting relation with the vibrator 42. A cap 43 is attached to the ceramic body 4| opposite the electrode 45, and has 4in its center a screw threaded collar 44. A second electrode 45, having a screw threaded projection 45 which cooperates with the collar 44, is adjacent to the vibrator 42 on the opposite side from the electrode 45. The screw adjustment for the electrode 45 allows an air gap 41 between the vibrator 42 and the electrode 45 to be adjusted. Adjustment of the air gap 41 in a well known way changes the operating frequency of the vibrator 42. 4

The upper portion of the supporting member or post I1 is bent at an angle of about 15 degrees from the vertical, so that the vibrator 42 rests in good thermal relation with the electrode 45, to allow its temperature to be accurately controlled. This also assures a fixed position for the vibrator 42. The entire weight of the vibrator 42 is not supported upon its active face against electrode 45, and the vibrator 42 is therefore more eilective in its operation. It is important in all forms of my invention that the vibrator 42 be maintained in good heat conducting relation with the supporting post I1, which should form the principal path for heat flow therefor.

In Fig. 5 an alternative form of piezo electric vibrator holder is illustrated. The vibrator 42 is pressed between an electrode 50 and the electrode 4|). A cap 5| is attached to the seramic body 4| opposite to the electrode 45. A spring 52 'between the electrode 50 and the cap 5| maintains a proper amount' of pressure between the electrodes. Shoulders 53 and 54, respectively on the electrode 5|) and the cap 5|, maintain the spring 52 in pressing relation therebetween. In this alternative form of vibrator holder itis to be noted that the vibrator 42 is again maintained in intimate thermal relation with the electrode 45 and with the supporting member I1 even though the electrode faces are reversed. In this case the supporting member |1 is not bent to any particular angle. since the spring 52 serves to maintain good thermal contact between the vibrator 42, the electrode 45 and the supporting post I1.

In Fig. 6 a crystal unit 55 of the type illustrated by Fig. 5 is shown in apparatus embodying a slightly di'erent form of my invention. In this modification many elements are similar to those illustrated in Fig. l and are given like reference characters. A'somewhat diilerent form of thermostat is utilized in this modification in order to provide greater stability in temperature control,

when the apparatus is subject to shock. A bimetallic member 5I is fastened at one end to the upper end of the supporting post I1 by a screw 52. The free end of the member 5I has a contact tip 53. which cooperates with an adjustable contact 54. The adjustable contact 54 is supported in the supporting member i1 and is insulated therefrom. A circuit extends from the heater 22 through the supporting member I1, through the screw 52, the bimetallic member 5|, the contact tip 53, the adjustable contact 54, the conductor 21, the terminal I3, through a source oi'- potential, not shown, through the terminal I2, and through the conductor 25 back to the heater 22.

'I'his construction of the bimetallic member 4|, lying parallel to the supporting member I1, allows the bimetallic member to be of greater length. whereby it is moreiexible. A permanent magnet 55 is fastened to the supporting member I1 in cooperating relation with the bimetallic member Il to provide snap action therefor, as explained above. The ilexibility o! the member Il allows a more positive snap action. The bimetallic member li is made to lie very close to the supporting member I1, so that it is closely responsive to the temperature thereof. The bimetallic member il is responsive, not only .to the temperature of the supporting member l1 bev tween the heater 22 and the device 0l, but is also responsive in a certain degree to the temperature of the supporting member il adjacent the piezo electric device il. While superior results have been obtained with the structure illustrated by Fig. 1, which is preferred, it appears that very good results are obtainable with a structure such as illustrated in Fig. 6.

In Fis. 7 there is illustrated an alternative structure in which a long iiexible bimetallic member is provided, which is responsive only to the temperature of the supporting member I1 between the heating means 22 and the piero electric device IO. ments are similar to those illustrated in the structure of Fig. l and are given like reference characters. A spirally arranged bimetallic member Il is supported at its central end on the supporting member I1. A contact 'Il on the outer end of the bimetallic member 1l cooperates with a ilxed adjustable contact 12 mounted on the support-` ing member I1. A permanent magnet 13, mounted on the supporting member I1, is arranged to cooperate with the outer end of the bimetallic member 'I0 to provide snap action. y v'Ihe circuit connections between the heater 22 and the bimetallic member 'Il are similar to those described in connection with Figs. 1 and '6.y

In this ligure many of the ele- 2.'In combination, a piezo electric vibrator to be maintained at a constant temperature, an electrode for said vibrator, means to maintain said vibrator and said electrode in intimate thermal relation, a heat conductive supporting post for said vibrator having a supported end and a tree end, means to attach said electrode to said free end and to maintain heat iiow to and from said vibrator principally through said supporting post, means to heat said supporting nmst between said supported end and said vibrator, and means to control the amount of heat applied by said heating means to said post in response to a thermaicondition ot said supporting post between said heating means and said vibrator, said post being of small cross section and having small mass whereby said vibrator quickly attains a constant temperature.

3. In combination, a hermetically sealed vessel, a piezo electric device within said vessel, an altelnating current circuit including said device and connections .therefor extending through the walls ot said vessel, a heat conductive supporting post for said device supported within said vessel, means to support said device on said post'and to maintain heat ilow to and from said device principally through said post, a resistance heater attached to said post in the path of said principal heat ow, and a thermostat attached to said post between said heater and said device responsive to the temperature of said post to connect a source of potential to said heater below a predetermined temperature o! said post.

In order to assure that the bimetanie member.

lll responds very closely to the temperature o1 the supporting member I1 between the heater 22 and the piezo electric device I0, an insulating hood 14, which is illustrated as partly brokeny away, may be arranged over the member 1l.

While my invention is especially adapted fn maintain constant temperature for a piezo electric vibrator, its scope is not limited to such use, since it is also capable oi' maintaining other devices at a constant temperature, such for example, as any instrument or device whose characteristics change undesirably with changes in maintained at a constant temperature, a heat conductive supporting post for said device having a supported end and a i'ree end, means to support said device on said free end and to maintain heat ilow to and from said device principally through said supporting post, a resistance heater attached to said supporting post between the supported end thereof and said device, and a thermostat attached to said post between said heater and said device responsive to the temperature of said supporting postto connect a source of potential to said heater below a predetermined temperature o! said post.

4. In combination, a hermetically sealed vessel, a. piezo electric vibrator within said lvessel, an al'- ternating current circuit including said vibrator and connections therefor extending through. the

[walls oi' said vessel, anvelectrode for said vibrator,

means to maintain said vibrator and said electrode in intimate thermal relation, a. heat conductive supporting post within said vessel having a supported endv and airee end, means to attach said electrode to said i'ree end and to maintain heat iiow to and from said vibrator principally through said post, means to heat said supporting post between said supported end and said vibrator, and means to control the amount of heat applied by said heating means to said post in response to a thermal condition of said sup-V porting post between Said heating means and -said vibrator.

5. AIn combination, a hermetically sealed vessel, a piezo electric device within said vessel, an alternating' current circuit including said device and connections therefor extending through the walls'ot said vessel, a supporting electrode for said device, a supporting member within said vessel having a portion ilxed thereto, means to. attach said electrode thereto at a substantial angle from vertical to maintain said device in intimate thermal relation with said electrode, means to maintain heat ilow to and from said device principally through said electrode and said supporting member, means to heat said supporting member between said fixed portion and said electrode, and means to control the amount of heat-supplied by said heating means in response to a thermal condition oi' said supporting member between said heating means and said device.

6. In combination, a hermetically sealed vessel, a piezo electric vibrator within said vessel, an a1- ternatlng current circuit including said vibrator and connections therefor extending through the walls of said vessel, a pair .of electrodes for said vibrator, means to press said electrodes against opposite iac'es of said vibrator, a heat conductive l supporting post within said vessel having a supported end and a ireeend, means to support said vibrator on said free end and to maintain heat flow to and from said vibrator principally through said supporting post, means to heat said supporting post between said supported end and said vibrator, and means to control the amount of heat supplied by said heating means in response to a thermal condition of said supporting post between said heating means and said vibrator.

7. In combination, a body whose characteristics change undesirably with changes in temperature, a supporting heat conducting post having a free end on which said body is supported in good heat conducting relation and having a supported end spaced from said body and said free end and in heat transferring relation with the surrounding regions of variable temperatures, said body being substantially insulated from said surrounding regions except through said post so that heat transfer between said body and such regions takes place principally through said supporting post, means in heat transferring relation with said supporting post for maintaining a part of said post between said supported end and said body at a temperature different'from the variable temperatures of said surrounding regions, and means responsive to a thermal condition of said supporting post between said body and said last means for controlling the operation of said last means.

8. In combination, a hermetically sealed vessel having a-wall portion affected by ambient temperature changes, a heat conductive supporting post within said vessel having one end supported from said wall portion and a free end spaced therefrom, a piezoelectric device within said -vessel supported on said free end in good heat conducing relation therewith, said device having an operating frequency subject to undesirable vari ation with changes in temperature, an alternating current circuit including said device and connections therefor extending through the walls of said vessel, said device being substantially insulated from the walls of said vessel except through said post whereby the heat transfer between said device and said post maintains said device and said post at substantially the same temperature, a resistance heater attached to said post between said device and said supported end, and a thermostat attached to said post between said heater and said device responsive to the temperature of said post to connect a source of potential to said-heater below a predetermined temperature of said post. said thermostat being adjusted to maintain said post, and consequently said device, at a temperature constantly higher than the varying temperatures o! said vessel and substantially constant.

9. In combination. a body whose characteristics change undesirably with changes in temperature, the region surrounding said body being subject to temperatures variable over a range, an elongated heat conductive supporting post having a free end and a supported end spaced from said free end and aiected by the varying temperatures of said surrounding region, means for supporting said body on said tree end in good heat conductingv relation therewith, said body being substantially insulated from said surrounding region except through said post so that the principal path of heat flow between said body and said surrounding region is through said supporting post, whereby said body and said free end o! said post remain at substantially the same temperature, means for maintaining the temperature of said supporting post between said supported end and said body at a value different from temperatures within said range, and means responsive to the temperature oi' said supporting post between said last means and said body for controlling said last means to maintain the temperature of said post between said last means and said body, and consequently the temperature of said body, substantially constant.

i0. In combination, a body whose characteristics change undesirably with changes in temperature, a chamber having walls surrounding said body, the region surrounding said chamber and the walls of said chamber being subject to temperatures variable over a range of temperatures, an elongated heat conductive supporting post having a free end and a supported end iixed to a wall o! said chamber, means for supporting said body on said free end of said supporting post in good heat conducting relation therewith. said body being substantially insulated from the walls o! said chamber except through said post whereby said body and said post remain at substantially the same temperature, means for maintaining the temperature oi' said post between said supported end and said body at a value diiferent from temperatures in said range, and means responsive to the temperature oi' said supporting post between said last means and said body for controlling said last means to maintain the temperature oi' said post between said last means and said body, and consequently the temperature of said body, substantially constant.

' CHARLES F. BALDWIN.

- .CERTIFLCATE 0F CORREcToN. Patent No. 2,501,007 l November 5, 19m.

^ CHARLES F. BALDWIN.

-It' is hereby certified that error appears in the printed specification of the above numbered patent requiring correctionras follows: Page 2, second column, line 52, for' "seramic" read --ceramic; pageh., first column, line [LO-1.1.1, claim 8, for "iconducing," read. conduvcting; page 5, second `column, line 19, beginning with"'5.' In combination strike out all to and including the word and period "post," inline 55, comprising claim 5; and

-9 Claims; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent office.

Signed and sealed this 12th day of January, A. D. l9li5.

A Henry VanArsdale, (Seal) Acting Commissioner of Patents.

,CERTIFICATE 0F CORRECTION. K November 5, 1911.2.

patent No. 2,501,007

^ CHARLES F. BALDWIN.

-It. `is hereby certified'thatl error appears in the printed specification of the ebove numbered patent requiring correctionas follows: Page 2, second column,` vline 52, for "seramic .read ceramic; pagell, first Column, line )lO-hl, claim 8,v for "conducing" I'ec conducting-F; page 5, second column, line 19p, beginning with "5; In combination strike out all to and including the word and perodjpost." in line 55, comprising claim 5; and

signed and Sealed this 12th day of January, A. D. 19M. i

Henry Van-Arsdale, (Seal) Acting Commissioner of' Patents. 

